1. Field of the Invention
The present invention relates to a process for the production of a semiconductor device. More particularly, the present invention relates to a process for a high precision forming of a resist pattern valuable for use as a mask at the step of selectively etching a semiconductor substrate, silicon oxide film or polycrystalline film (generally called "workpiece" hereinafter) or injecting ions into the workpiece in the production of a semiconductor device such as an LSI. Namely, the present invention relates to an improvement in the resist-forming process, and the development process for forming a resist. The present invention also relates to an apparatus for carrying out the production process of a semiconductor device, particularly a developing apparatus for developing the exposed resist coating.
2. Description of the Related Art
For the formation of a semiconductor device, the patterning of a silicon oxide film, a polycrystalline silicon film, an aluminum film or the like is carried out by etching, and a photoresist material (photosensitive resin material) having a high resolution, high etching resistance, and high sensitivity is used for fine patterning operation. In general, patterning of the workpiece such as a silicon oxide film is conducted according to the procedures shown in FIG. 1. Namely, first a photoresist film is formed on the workpiece. As the negative-working photoresist material suitable for use for this purpose, there can be mentioned, for example, polymeric materials such as a polystyrene and rubber type material. The photoresist material is coated on the workpiece by the spin coating method to form a photoresist film, and the formed photoresist film is then exposed to a pattern of light to which the photoresist material is sensitive, whereby a latent image corresponding to this pattern is formed in the photoresist film. Where the exposure light source uses ultraviolet rays, this patterning exposure is effected by the entire surface light exposure using a mask having a predetermined pattern, which is placed on the photoresist film. Where the exposure light source uses a high-energy radiation such as an electron beam (EB), the patterning exposure is directly carried out by using an EB exposure apparatus. After the patterning exposure, the exposed photoresist film is developed. The development is carried out, for example, by immersing the workpiece in a liquid developer such as an organic solvent, for example, esters and alcohols, or an aqueous alkali solution. As a result of this development, the unexposed area is dissolved and removed, and thus a negative resist pattern is obtained. In the usual resist-forming process, rinsing is generally carried out for removing the adhering liquid developer, followed by drying. Then, the workpiece as the substrate is selectively etched by using the obtained resist pattern as a mask. This etching is performed by the dry process or the wet process according to the characteristics of the photoresist material. Namely, a desired resist pattern can be formed on the workpiece through the series of the above-mentioned process steps.
Nevertheless, this conventional resist-patterning process is defective because in some resist processes the development is attained only with the use of an organic solvent as a developer. In such processes, if it is intended to conduct a fine patterning of resist, a deformation or shift occurs in the obtained resist pattern. These problems will now be described with reference to the resist-patterning process using a negative photoresist material (see FIGS. 2A through 2E).
First, as shown in FIG. 2A, a negative photoresist material is coated on a film 40 to be processed (aluminum film in this case), which is formed on a semiconductor (silicon) substrate 50, by a spincoating method, to form a photoresist film 41. The photoresist material used is chloromethylated polystyrene, and the thickness of the formed photoresist film is 1.5 .mu.m.
Then, as shown in FIG. 2B, patterning exposure is carried out at 1 .mu.m-line and 1 .mu.m-space by using an electron beam as the light source. This light exposure causes the photoresist film 41 of the exposed region to be insoluble by the liquid developer to be used at the next step.
After the patterning exposure, as shown in FIG. 2C, the workpiece is immersed in a liquid developer and the photoresist film 41 of the unexposed region is dissolved and removed. The liquid developer used is a mixture of isoamyl acetate and ethyl cellosolve (9:1).
Then, the workpiece is drawn up from the liquid developer and is rinsed and dried (not shown in the drawings), whereby a negative resist pattern 41 as shown in FIG. 2D is obtained. In principle, the resist pattern should be formed at the position indicated by dot lines, but because of a meandering caused by a swelling of the resist material, the resist pattern 41 is shifted to the right and is inclined. From our experiments, it has been confirmed that the shift of the resist pattern 41 is about 0.3 .mu.m on the lower end and about 0.5 .mu.m on the upper end. In some cases, the resist pattern 41 is caused to shift to the left and is inclined, as shown in FIG. 3, or when the aspect ratio of the resist pattern 41 is large, as shown in FIG. 4, shoulders of adjacent patterns overlap each other. The shift and wavy deformation of the resist pattern 41 shown in FIG. 2D will become more apparent from the perspective view of FIG. 5.
If the film 40 to be processed is etched by using this defective resist pattern as the mask, the film 40 is patterned only in the meandering state with a shift of about 0.3 .mu.m, as shown in FIG. 2E, and the presence of this defect results in a reduction of the yield of the final product.
In the resist-patterning process using a positive photoresist material such as polymethacrylate, since the pattern-left (i.e., remaining resist pattern) area is large, the problem of a formation of cracks on the pattern edge often arises, due to a swelling of the resist with an organic solvent. More specifically, where a rectangular window 42 indicated by dot lines in FIG. 7 is opened on the positive photoresistive film 41 on the film 40 to be processed, as shown in FIG. 6, a deformation of the window is caused by a swelling of the resist resin, and cracks 43 are formed on the-pattern edge.
Some conventional techniques concerning improvements of the developing process are known but they are essentially different from the present invention and do not contribute to the completion of the present invention. For reference, these techniques will now be briefly discussed.
The invention disclosed in Japanese Unexamined Patent Publication (Kokai) No. 63-233530 relates to a pattern-forming process, especially a pattern-forming process valuable for obtaining an overhanging photo resist by the lift-off process. According to this invention, the development using an alkali liquid developer is once interrupted, the used liquid developer is washed and removed with pure water, and the development is conducted again with the same liquid developer. If the development is thus interrupted, even when the development-interrupted portion is subjected to another development, the development speed is lower than the usual development speed, and accordingly, the desired overhanging pattern can be easily formed.
The invention disclosed in Japanese Unexamined Patent Publication (Kokai) No. 64-61915 also relates to a pattern-forming process. According to this invention, in the process where a positive resist film is light-exposed, developed, water-washed and dried, the operation of reducing the developing speed on the surface of the positive resist or on the surface of the new resist formed by the development is repeated a plurality of times during the development using an alkali liquid developer, or before and during the development. Water washing and drying after the interruption of the development are effective as the means for reducing the developing speed. If the developing speed of the region not irradiated with electron beams is thus reduced, the proximity effect is reduced and a pattern having a high dimensional precision and a high contrast can be formed. Nevertheless, it should be noted that, since the pattern-forming processes described in this and the above-cited Japanese Kokais do not use an organic solvent as a developer, they cannot avoid the problem of resist swelling.
With regard to the problem of resist swelling, of course, this swelling can be controlled by changing the composition of the liquid developer or the developing temperature or by changing the composition of the photosensitive polymer used as the photoresist, but a satisfactory effect cannot be obtained. Therefore, the development of a process for the production of a semiconductor device in which, when developing a latent image of a photoresist film, the visualization is accomplished at a high precision and a film to be processed can be patterned by using the formed photoresist film as a mask, is desired.